Mercaptan conversion



June 30, 1936. P, K FRQLICH E1- AL 2,045,766

MERCAP'QIVAN CONVERSION Filed Aprile, 1952 Q 2% Ky gw e INVENToRsZ39/@Bf 94/ M KLMORNEY oxides or suliides of the VI group metals, theVorganic sulfur compounds.

Patented l June 30, 1936 vP'A'riiN'l .OFFICE MERCAPTAN CONVERSION Per K.Frolich and Peter J. Wiezevich, Elizabeth, N. J., assignors to StandardOil Development Company, a corporation of Delaware Application April 8,1932, Serial No. 603,922

22 Claims.

This invention relates to the production, from mercaptans, of relativelyhigher molecular weight organic products by a catalytic process, andmore especially to the production of relatively higher molecular weightmercaptans and other The reactions involved in producing these organicsulfur compounds may b'e represented as follows:

The formation of higher mercaptans and thioethers from mercaptans asindicated in reactions 1 and 2 may be classified as dehydrunsulngreactions, i. e. which involve removal of hydrogen sulfide. Theformation of aldehydes,. disuldes and thio-esters as indicated inreactions 3,* 4 and 5 may be classified as dehydrogenation reactions.Products corresponding to those indicated in the above equations may beobtained by subjecting a mercaptan to suitable conditions of heat andpressure in the presence of dehydrogenating and/or dehydrunsulngcatalysts.

Suitable dehydrunsulng catalysts are described in the co-pendingapplications Ser. No. 585,l56,.led January 6, 1932, b y Seaman andHuffman, and Ser. No. 605,783 filed April 16, 1932, by Per K. Frolich.Among such catalysts may be mentioned substantially all the metallicsuldes, especially those of the heavy metals such as copper, mercury,tin, lead, chromium, tungsten, molybdenum, iron, cobalt and nickel. Thesuldes may be used alone or in admixture with each other or with othersuitable suldes such 4as those of cadmium, strontium, barium andaluminum. 'I'he stability of these catalysts may be aided bydistributing them upon activated carbon or other.

Suitable dehydrogenation vcatalysts include those normally used 'for theproduction of esters fromxalcohols. Among the satisfactory catalysts isone composed of metallic oxides or suldes mixed in suitable proportions.For example, the

metals of the iron group, or copper may be used in mixtures varyingwidely in composition. Other metals, oxides, or suldes favoringdehydrogenation may be used in admixture with or in vsubstitution forany of the above mentioned catalytic components. A relatively smallamount of an ,I oxide of the alkali or alkaline earth metals may 5 alsobe added. Mixed dehydrogenating and devhydrunsulilng catalysts may alsobe used.

While both alkyl and aryl mercaptans may be used vin this process, therelatively low molecular Weight mercaptans obtained from petroleum oils10 such as sour cracked naphthas are especially suitable.. Thesemercaptans may be readily separated from naphthas and other hydrocarbonoils by washing with an aqueous caustic solution and subsequentlydistilling the mercaptansfrom this solution with steam. The product thusobtained constitutesl a rather complex mixture of mercaptan's' whichconsists primarily of methyl, ethyl, propyl, and butyl mercaptans. Thisproduct may be used directly as a feed stock in the herein dis- 20closed process. However, it may be desirable to use as a feed stock adistillate fractionboiling within a range of about to 50 C., as optimumconditions'of operation may vary slightly with increasing boiling pointsof the mercaptans used. 25

For example, the fractions boiling below 50 C... between 50 and 75 C.,and above 75 C. may be used separatelyk to advantage in the presentprocess.

Regarding operating conditions, it is preferred to use a reactiontemperature at which the mercaptans treated are substantially completelyin vapor phase. The reaction temperature depends upon the activity ofthe catalyst used andy on the time of contact, and should not be so highas to cause undue decomposition of the feed stock or product as'by theformation of olefinesA or heavy polymers, or the' formation of excessiveamounts of fixed gases. The preferred reaction temperature generally isbetween about 300 and 450 C. 40 but it may be lower or higher, dependingupon the activity of the catalyst and other operating conditions; forexample, temperatures from about 200 or 250 C. to 500 C. may be usedunder suitable operating conditions. Pressures above atmospheric aregenerally preferred because of their retarding effect on undesirableside reactions such as the formation of oleflnes and of gaseousdecomposition products. Pressures of 10, 50, 100, 200 atmospheres orhigher may be `used and the more elevatedpressures are preferred. Thereaction vessel should be constructed of or lined with; materialresistant to the corrosive action of the reagents and products,especially to hydrogen sulfide and mercaptans. 55

from these gases by rectification, or by scrubbing with an alkalineagent, or a hydrocarbon liquid such as naphtha, kerosene or gas oil.

It will be understood from vthe above descrip-v tion that it is.possible by this catalytic opera.- tion to obtain at least three majorproducts from a mercaptan; namely, higher mercaptan, ester, anddisulfide, with twice the number of carbon atoms of the originalmercaptan. The process is further complicated however both on accountof, the simultaneous occurrence of side reactions and because the newmercaptan formed is subject to the same catalytic changes as the oneoriginally used as the raw material.V Thus the butyl mercaptan formedfrom ethyl mercaptan will give rise to the formation of butyl aldehydesand to still higher esters, disuldes, mercaptans, etc. Although allthese reactions proceed to some extent under reaction conditionsfavoring any one of them, a certain` amount of selectivity may beobtained by varying the type'of catalyst employed and by properlyregulating the concentration ofthe reactants and products in thereaction zone. According to this method o f operation it is possible tobring these more or less haphazard reactions under control and'to favorthe production of one particular compound or at least of one particulartype of compounds.

Products containing Oxy-organic compounds, such as alcohols,oxygen-containing esters, aldehydes, ketones and the like, and mixed oxyand organic sulfur compounds such as thio-esters and the like, may belobtained by passing a mixture of steam and mercaptan over similarcatalysts. Likewise. alcohols may be introduced with the mercaptans fedtothe reactor. Air and/or other oxidizing gases may also be supplied tothe reaction zoneinlimited amounts, and aid especially in the productionof disuldes by dehydrogenation of mercaptans,

In this process the starting material may con'- Y Lsist of a lowermercaptan in admixture with water vapor, carbon monoxide, or hydrogen,according to the products desired. -For example, if .it

is desired'to suppress aldehyde, ester and disulfide formation and tofavor the production of higher mercaptans and/or thio-ethers, hydrogenmay be introduced with the lower mercaptan into the reaction zone. Theincreased partial pressure of hydrogen reduces the tendency fordehydrogenation to aldehyde without however interfering lwith thecondensation to thio-ethers -or higher"m'ercaptans, the net result beingthat thio-ethers and higher mercaptans rather than 'aldehydes and esterspredominate in the'product.

It is desirableat theY same time to use a catalyst which favorsdehydrunsuliing rather than dehydrogenation. To further facilitate theformation of higher mercaptans and thio-ethers, carbon monoxide may beintroduced with the reaction mixture in which case the hydrogen sulfideformed v during the condensation is removed according to the reactionH:S+CO- COS+H: Since this reaction produces hydrogen itA isobsulfldesand the like.

viously possible, when carbon monoxide is used, to accomplish the sameresult with respect to the suppression of aldehyde and ester formationwith less hydrogen in the initial gas mixture.

Conversely it is possible to reduce the forma- 5 tion of thio-ethers andhigher mercaptansI and thereby favor aldehyde and ester formation byintroducing hydrogen sulfide with the mercaptan. Dehydrogenatingcatalysts are also preferred.

The concentration of hydrogen andhydrogen sulde in the reaction mixturemay be controlled as desired by proper regulation, treatment andrecirculationof the uncondensed gaseous reaction products. Additionalhydrogen or hydrogensulfide above that available in the recirnculated l5gases may of course be a'dded if desired. It is also generally desirableto lmaintain an appreciable concentration of say 10 to 30% of gaseousolefines in the recirculated gases as the presence of olenes may,depending upon the conditions of 20 operation, exert a retarding effectupon olei'lneformation by the splitting of hydrogen sulfide from asingle mercaptan'molecule.

The following examples illustrate methods under which the hereindisclosed process may be 25 conducted. y

1. Asour crackedI gasoline is washed with aqueous caustic soda.A Theresulting aqueous layer is then distilled with steam andi a distillatecontaining an oily layer of mercaptans insoluble in 30 water isobtained. These mercaptans are redistilled and the fraction distillingbetween 30 and 50 C. is separately recovered. This fraction is passed at250 C. over active carbon. It is then cooled to 50 C. and a small amountof -oily con- 35 densate forms and is separately removed. The remaininguncondensed vapors are then passed at a temperature of 350 C. over acatalyst consisting of one part of cadmium sulfide, one part zincsulfide and one part activated charcoal. The product is then cooled toatmospheric temperature and a liquid product is obtained which consistslargely of thio-ethers. The uncondensed gases obtained consist primarilyof hydrogen, hydrogen sulde, and olenes.

2. The process described in Example lis conducted under the sameconditions shown therein except that gaseous reaction products insuiiicient amount to maintain the total feed in vapor phase arerecirculated with added mercaptans over the catalyst at a reactionpressure of about 100 atmospheres. The liquid product contains a mixtureof higher mercaptans, thio-esters, thioethers and poly-sulfides withsome unreacted lower mercaptans which may be separated andre- *used inthe process.

3. The process is conducted las, described in Example 2 with theexception that the concentration of hydrogen sulfide in the recycled gasis maintained below, about 5%. The resulting liquid product contains alarger proportion of thioethers and higher mercaptans, and a smalleramount of esters, than in Example 2.

4. The process is repeated according to Example 2 with the exceptionthat the concentra' tion of hydrogen in the recycled gas is maintainedbelow about'1v0%. The resulting product cont'ains a larger proportion ofthio-esters with lesserv amounts of higher mercaptans, thio-ethers,poly- The drawing is an illustration. of a flow plan for the mercaptanconversion process with especial reference to the production ofthio-ethers and disulildes. Various alternative procedures for theprocess flow plan and treatments of the 75 mercaptans.

products which may be desirable in connection with the variousmodifications of the mercaptan conversion process herein disclosed willbe readily apparent. The mercaptan supply may consist of either a puremercaptan or a mixtureof merelevated' temperature, insuicient tov causeappreciable reaction of the mercaptan, over van active adsorbent such asactivated carbon, decolorizing clays, etc., as shown in Example 1,above. The purification may also rbe conducted by treating the mercaptanvapor with an aqueous concentrated zinc chloride solution or bytreatment in liquid phase with sulfuric acid, aluminum chloride anddecolorizing clays, phenol and the like. The purified cut with orwithout addition of .recirculated gases yor other gases is passed atsuitable. temperatures and pressures through a reaction zone containinga suitable catalyst. Theproduct from this zone is then cooled,preferably under rectifying conditions, and three fractions are secured.The least volatile or bottoms fraction contains mercaptan conversionproducts such as thio-ethers, dsulfides and the like, and The mercaptansare removed by extraction. with a suitable solution such as leadacetate, sodium plumbate, or an alkaline agent such as a caustic sodasolution, triethaholamine and the' like, and maybe recovered from thissolution by suitable means such as steam distillamove heaviermercaptans, to the mercaptan conversion step.

Theresidue from this extraction step may thenv be fractionated bydistillation by which the lighter thio-ethers are secured as adistillate andthe less volatile disuldes and other organic sulfurcompounds comprise the distillation residue.

The liquid distillate of the product rectification consists mainly ofunconverted mercaptans which may be recirculated preferably afterrectication and purification to the mercaptan conversion process. I

The uncondensed gases consisting primarily of hydrogen, hydrogensulfide, olenes and mercaptan vapors may be bled olf or recirculatedwith suitable treatment to control the concentration of these componentsin the reaction zone. Any one or more of these components may beseparately removed by suitable extraction methods from the gases and maybe Withdrawn or recirculated to the mercaptan conversion process.

'I'he following catalysts are also mentioned as examples of thosesuitable for the above described process:

5. A catalyst containing 50% iron sulfide and l 50% manganese sulfide isobtained by co-precipitation with hydrogen sulde from an aqueoussolution of the sulfates.

6. A catalyst containing parts of cadmiumv of zinc, manganese andchromium in equal molalproportions with s'uiiicient water to make astiff paste. This paste is passed through a pill, machine and theresulting` pellets are dried.

Such mixtures are preferably distilled to While the initial materialsused in the preparation of catalysts suitable for this process have beendescribed, it is understood that changes may occur in the composition ofthe catalyst during the process with the formation of higher or lower 5suldes, oxides, etc. and that this invention in-` cludes the use of allsuch catalysts in Whatever form they may exist during the process.

This process is especially suitable forthe conversion of methylmercaptan to ethyl mercaptan. 10

' The latter may then beconverted to ethyl thioether, which is suitablefor use in paints, varnishes, lacquers, rubber compositions, Grignardsyntheses, in lresin preparatiomas a solvent for resins,A and for manyother purposes. l5 Where the mercaptans to be converted are secured frompetroleum fractions it is generally preferable to subject them to aninitial treatment for the removal of undesirable components or catalystpoisons. Although the nature of the process and thereactions involvedmay be readily understood on. the basis of the reaction mechanismsdescribed herein, the invention is not to be limited to any theory orexplanation of the steps involved or to any 25 examples4 which are givensolely for purpose of illustration, but only bythe following claims inwhich We wish to claim all novelty insofar as the prior art permits.

We claim: y 30 1. Theprocess which comprises passing mercaptans at areaction temperature over a deliydrunsuliing catalyst under suiiicientpressure for lsubstantial conversion into relatively higher molecularweight mercaptans and other organic 35 sulfur compounds.

2. Process for the conversion of mercaptans into relatively highermolecular weight mercaptans and other organic sulfur compoundscomprising passing a mercaptan at a reaction tem- 40 perature and apressure raised substantially above atmospheric over a dehydrunsulngcatalyst. v

3. -Process according to claim 2 in which the catalyst comprises a metalsulfide.

4. Process according to claim 2 in which the 45- into relativelyhighermolecular Weight mercap- 55 vtans and other organic sulfur compoundscomprising passing a mercaptan in vapor phase at a reaction temperatureand a pressure substantially above .atmospheric over a vdehydrunsulflngcatalyst. 60 8. Process for conversion of mercaptans intov relatively.higher molecular Weight mercaptans and other organic sulfur compoundsvcomprising passing'a mercaptan vin vapor phase at a tem` peraturebetween the approximate limits of 250 and 500 C. and a pressure aboveabout 10 atmospheres over a dehydrunsulflng catalyst.

9. Process according 'to claim 8 in which the uncondensed gaseousproducts are repassed over the catalyst with added mercaptan.

10. In the conversion of mercaptan into relatively higher molecularweight mercaptans and other organic sulfur compounds by passing saidmercaptan at a reaction pressure and tempera-v ture over adehydrunsulfng catalyst, an yim 75 provement favoring the production ofhigher mercaptans comprising conductingthe reaction in the presence ofadded hydrogen. y

11. In the production of relatively higher molecular weight mercaptansand other organic sulfur compounds by the catalytic dehydrogenation anddehydrunsulng of 7lower molecular weight mercaptans at reactiontemperatures and pressures, an improved method for decreasing theformation of higher mercaptans and increasing the proportion of estersin the product, comprisin the presence ling oxygen to the mercaptans arefed into the rcaction zone along with the mercaptan feed stock,

whereby mixed organic Oxy-sulfur compounds are produced.

15. 'I'he process which comprises passing a mercaptan feed stock atreaction temperature over a dehydrunsullng and dehydrogenating catalyst,

removing from the reaction products higher mercaptans, thioethers,thio-aldehydes, polysulfides and thio-esters, and recycling uncondensedgases and unreacted raw material.

16. Process according to claim 15, in which the amount of olefines,hydrogen sulfide and hydrogen in the uncondensed gases isregulated'before recycling, in order tocontrol the proportion of highermercaptans, thioethers, thio-aldehydea polysuldes and thin-esters to beproduced.

17. Process according to claim 15, carried out at a, pressure aboveatmospheric.

18. Process according 'to claim 15, in which petroleum mercaptans areused as the original feed stock and in which said feed stock is puriedbefore passing to the catalytic reaction zone.

19. Process for converting mercaptans into higher molecular weightmercaptans, which comprises passing a mercaptan feed stock at a reactiontemperature over a dehydrunsulfing catalyst at a pressure substantiallyabove atmospheric.

20. Process for converting mercaptans intoV relatively highermolecularweight thioethers, which comprises first converting said mercaptans intohigher molecular weight mercaptans by subjecting them to heat treatmentunder pressure in the presence of a hydrunsulng catalyst and thenconverting said higher molecular weight' mercaptans into correspondingthioethers.

21. 'I'he process for the conversion of mercaptans into relativelyhigher molecular weight mercaptans' and other organic sulfur compounds,which comprises purifying said mercaptans, then passing them at areaction temperature and pressure over a dehydrunsulng catalyst,subjecting the reactionl products to rectification whereby threefractions are obtained, namely, uncondensed gases, a mercaptandistillate and heavier jbottoms, recirculating at least part of theuncondensed gases to control the trend of the reactions in the reactionzone, recirculating the mercaptan distillate which comprises chieflyunconverted mercaptans, extracting the rectification bottoms to removemercaptans, subjecting said mercaptans to rectification to remove highermolecular weight mercaptans and recycling the lower molecular weightmercaptans, and distilling the extraction 'residue whereby a thioetherdistillate and a polysulde residue are obtained.

22. The process for treating mercaptans, which comprises subjecting themto catalytic reaction' under suiicient pressure for substantialproduction of higher molecular Weight organic sulfur compounds in thepresence of a low molecular weight decomposition product of mercaptansto favor the formation of high molecular weight reaction products.

Y PER K. FROLICH.

PETER J. WIEZEYICH.

